Many of the commonly used secondary measures for the determination of biopolymer concentration, such as molar absorptivity, molar refractive index and specific volume, are found not to be firmly established on the basis of mass of substance in solution. In order to correct this situation the following procedures are proposed. 1. To establish the best conditions for dry weight determination. 2. To find the correct correlation of secondary measures, especially of membrane proteins in detergent solution, inherently complex substances such as viruses and other nucleoproteins, and glycoproteins, with the concentration obtained from dry weight.